The concept of ‘openness of the Green Belt’, and its relationship (if any) to visual impact, has been a point of constant discussion. Although identified in the NPPF (and preceding PPG2) as one of the essential characteristics of Green Belts, ‘openness’ is not formerly defined. The stance of the Higher Courts on the interpretation of openness and its correlation with visual impact can, however, be better understood through examination of the appurtenant case law as outlined below.
Paragraph 145 of the NPPF states that:
“A local planning authority should regard the construction of new buildings as inappropriate in the Green Belt. Exceptions to this are:
g) limited infilling or the partial or complete redevelopment of previously developed land, whether redundant or in continuing use (excluding temporary buildings), which would:
not have a greater impact on the openness of the Green Belt than the existing development; or
not cause substantial harm to the openness of the Green Belt, where the development would re-use previously developed land and contribute to meeting an identified affordable housing need within the area of the local planning authority.”
Heath and Hampstead Society v London Borough of Camden 2007 and Timms/Lynn v Gedling BC 2013 originally suggested that ‘openness' is strictly related to the absence of buildings or development and that the extent to which a site is visible from public vantage points and the extent to which a proposed development would be visually intrusive are separate from openness.
In Timmins v Gedling Borough Council  EWHC 654 (Admin), Green J went a stage further holding, not only was there “a clear conceptual distinction between openness and visual impact”, but that it was:
“wrong in principle to arrive at a specific conclusion as to openness by reference to visual impact.”
This was subsequently disapproved by Lord Justice Sales who upheld a decision to refuse permission for a proposal to replace a mobile home and storage yard with a residential bungalow in Turner v Secretary of State for Communities and Local Government  EWCA Civ 466:
“The concept of ‘openness of the Green Belt’ is not narrowly limited to the volumetric approach. The word ‘openness’ is open-textured and a number of factors are capable of being relevant when it comes to applying it to the particular facts of a specific case. Prominent among these will be factors relevant to how built up the Green Belt is now and how built up it would be if redevelopment occurs…and factors relevant to the visual impact on the aspect of openness which the Green Belt presents.”
It was considered that the ‘visual impact is implicitly part of the concept of openness of the Green Belt’ and it relates to the capacity of the Green Belt to fulfil its purposes.
Notwithstanding this, the Supreme Court recently provided seemingly the most relevant guidance on openness in R (on the application of Samuel Smith Old Brewery (Tadcaster) and others) (Respondents) v North Yorkshire County Council (Appellant)  UKSC 3. Overturning the Appeal Court ruling, the Supreme Court found that, on a true reading of the NPPF, the visual quality of a landscape is not in itself an essential part of the openness for which the green belt is protected.
Lord Carnwath, who gave the court's judgment, noted that one of the primary objectives of green belt policy, since its inception, was "to prevent urban sprawl while keeping land permanently open".
The reference to "openness" in paragraph 146 of the 2019 NPPF, he added, "does not imply freedom from any form of development" and "is not necessarily a statement about the visual qualities of the land".
Although visual impact may, in some cases, be relevant to the question of whether openness will be preserved, the weight to be given to it was "a matter of planning judgment, not law".
Paragraph 5 of judgement provides:
“The PPG included a fuller statement of certain “objectives” for the use of land within defined Green Belts, including (for example) providing opportunities for access to open countryside, and retaining and enhancing attractive landscapes (para 1.6), but adding:
“The extent to which the use of land fulfils these objectives is however not itself a material factor in the inclusion of land within a Green Belt, or in its continued protection. For example, although Green Belts often contain areas of attractive landscape, the quality of the landscape is not relevant to the inclusion of land within a Green Belt or to its continued protection. The purposes of including land in Green Belts are of paramount importance to their continued protection, and should take precedence over the land use objectives.” (para 1.7)
It is clear therefore that the visual quality of the landscape is not in itself an essential part of the “openness” for which the Green Belt is protected.”
Despite Lord Carnwath’s ruling, it would appear prudent to assess both spatial and visual aspects within the context of the site to ensure that any relevant considerations likely to form part of the ‘planning judgement’ are clearly understood.